This invention relates generally to centrifugal blowers or fans, and it relates more particularly to the structure of the housing of a single-stage, multiple outlet centrifugal blower.
Centrifugal blowers, ventilators, fans, pumps, and other similar apparatus are conventionally designed and constructed to raise the pressure of an incompressible fluid and to discharge the fluid at a desired volume rate of flow into a pipe or duct to which the outlet of the apparatus is connected. The fluid, in order to move continuously through the discharge duct of the connected system, has to be supplied with enough energy to overcome the downstream backpressure at the outlet of the apparatus. This backpressure is the sum of the pressure drop in the downstream system caused by the fluid resistance of the discharge ducts and the total fluid pressure (velocity pressure plus static pressure) at the exit end of the ducts.
It is relatively easy to design or to select a centrifugal pump, blower, or the like capable of discharging fluid through a single outlet at a pressure and volume flow that match the requirements of any system having only one discharge path and one exit. However, this is not true if the downstream system has two or more separate branches which are required to deliver different volume flows at various different pressures. A practical example of the latter system is found in electric drives on large, self-propelled, off-highway traction vehicles where a prime mover-driven blower supplies air for cooling both an electric current generator (or alternator) and a plurality of traction motors associated with the wheels of the vehicle. The volume flow rate of air required to cool the motors can be appreciably higher than the volume flow rate of air that cools the generator, and the backpressure of the air that cools the motors can vary from one size vehicle to another. When a prior art single-outlet blower is used, the ductwork between the blower outlet and the generator has heretofore included an artificial restriction that provides relatively high resistance to the flow of air in this branch of the system, thereby reducing the volume flow rate of cooling air that flows to the generator compared to the volume flow of air in the other branch of the ductwork that is connected between the same outlet and the traction motors. Such a restriction results in an undesirable loss of power, and it reduces the efficiency of the system.